The cestodes Taenia solium (pork tapeworm) and Taenia saginata (beef tapeworm) cause the two major forms intestinal taeniasis in humans (Pawlowski, Z. S., 1990, "Cestodiases: Taeniasis, Cysticercosis, Diphyllobothriasis, Hymenolepiasis, and Others," Tropical and Geographical Medicine (Warren, K. S., and Mahmoud, A. F., eds.) pp. 490-504, 2nd ed., McGraw Hill, New York). Both human and swine cysticercosis are acquired through ingestion of T. solium eggs. In contrast, ingestion of T. saginata eggs causes cysticercosis in cattle, but not in humans. Thus, the epidemiological importance of taeniasis produced by T. solium is not the same as that produced by T. saginata, since the former causes human cysticercosis, while the latter does not infect humans in it metacestode stage.
Cysticercosis caused by ingestion of T. solium eggs is a disease of particular importance in many developing countries (Flisser, A., 1988, Parasitol. Today, 4:131-137; Mahajan, R., 1982, "Geographic Distribution of Human Cysticercosis," Cysticercosis: Present State Knowledge and Perspectives (Flisser, A., et al., eds.), pp. 39-42, Academic Press, New York). Neurocysticercosis is the most common and serious form of cysticercosis in humans (Flisser, A., 1988, supra; Gemmell, M., et al., 1983, "Guidelines for Surveillance, Prevention and Control of taeniasis/cysticercosis," VPH/83.49, World Health Organization, Geneva, 1-207). Human cysticercosis is a serious problem for public health in developing countries, and implies heavy economic losses as a result of medical expenses, absenteeism and a gradual loss of the general state of health of the sick person. Furthermore, swine cysticercosis is a serious economic problem for pork production due to the confiscation of infected animals.
Cysticercosis was essentially eliminated from the developed countries at the beginning of the century by improving health infrastructure, health education and personal hygiene. Although this same approach would put an end to the present problem in underdeveloped countries, it is virtually impossible to apply these measures due to the high cost implied in the construction of suitable latrines in all the endemic regions, the low existing level of education and the difficulty of modifying habits and practices associated with food and health in communities where cysticercosis is endemic. Recently, cysticercosis has emerged again as a pathogen in some developed countries due to migration and tourism (Craig, P. S., et al., 1988, Trans. Royal Soc. Trop. Med. Hyg. 82:268-274; Earnest, M. P., et al., 1987, Rev. Infect. Dis., 9:961-979) further underscoring the need for control of this disease.
Cysticercosis normally results from ingestion of infected pork or from ingestion of other material contaminated with T. solium eggs. Because T. solium eggs are commonly shed by individuals harboring an adult tapeworm (Sarti, E. J., et al., 1988, Trop. Med. Parasitol. 39:194-198; Sarti, E., et al., 1992, Am. J. Trop. Med. and Hyg. 46:677-685; Schantz, P. M., et al., 1992, NEJM 327:692-695), control of this disease is largely dependent on reducing the contamination of water and food with T. solium eggs. In fact, recent epidemiological studies have shown that individuals with taeniasis are the principal risk factor for the propagation of cysticercosis (Sarti et al., 1994, Trans. Royal Soc. Trop. Med. Hyg. 88:49-52; Diaz-Camacho et al., 1991, Amer. J. Trop. Med. Hyg. 45:522-531).
Identification and treatment of human carriers of adult state tapeworms is a promising strategy to decrease the incidence of cysticercosis. However, identification of human carriers is complicated by the fact Taenia carriers are frequently asymptomatic (Faust, E. C., et al., 1970, Craig and Faust's Clinical Parasitology, pp. 502-507, 785-790, Lea and Febiger, Philadelphia; Gemmell, M., et al., 1983, supra; Pawlowski, Z. S., 1990, supra). Moreover, diagnosis of taeniasis is routinely performed by coproscopical examination (Faust, E. C., et al., 1970, supra), which has a low sensitivity of detection (Farahmandian, I., et al., 1973, Trop. Geogr. Med. 25:171-173). Because T. solium and T. saginata eggs have identical morphology (Faust, E. C., et al., 1970, supra, Gemmell, M., et al., 1983, supra), this method also does not allow the clinician to distinguish eggs of the Taenia species. While high sensitivity has been achieved with an ELISA for coproantigen detection of human Taenia carriers (Allan, J. C., et al., 1990, Parasitology 101:473-477), this assay cannot distinguish T. solium from T. saginata (Allan, J. C., et al., 1990, supra).
Diagnosis using repetitive DNA probes, which results in improved sensitivity, has been successful in Trypanosoma cruzi (Gonzalez, A., 1984, Proc. Natl. Acad. Sci. USA 81:3356-3360), Leishmania (Wirth, D. F., and Pratt, D. M., 1982, Proc. Natl. Acad. Sci. USA 79:6999-7003), Plasmodium falciparum (Barker, R. H., et al., 1986, Science 231:1434-1436), Entamoeba histolytica (Edman, U., et al., 1990, J. Exp. Med. 172:879-888; Garfinkel, L. I., et al., 1989, Infect. Immun. 57:926-931; Samuelson, J., et al., 1989, J. Clin. Microbiol. 27:671-676), and Onchocerca vulvulus (Erttmann, K. D., et al., 1987, Nature 327:415-417; Shah, J. S., et al., 1987, Am. J. Trop. Med. Hyg. 37:376-384) infections, among others. Most of these probes are repetitive sequences, resulting in highly sensitive hybridization assays. Moreover, the cost of these assays (US $0.17 per assay) is approximately half that of microscopic examination (Barker, R. H., et al., 1994, Int. J. Epidemio. 23:161-168).
Use of T. solium or T. saginata genomic DNA or species-specific taeniid DNA sequences to detect taeniid DNA has been described (McManus, 1990, Rev. Sci. Tech. Off. Int. Epiz. 9:489-510; McManus, D. P. et al., 1989, Acta Leiden 57:81-91; Harrison, L. J. et al., 1990, Parasitology 100:459-461; Flisser, A., 1990, Ann. Parasitol. Hum. Comp. 65:95-98; Rishi, A. K. and McManus, D. P., 1988, Parasitology 97:161-176; Rishi, A. K. and McManus, D. P., 1987, Lancet i:1275-1276). While the species-specific sequences can detect isolated taeniid DNA with at last some sensitivity and/or specificity, the sequences have either provided insufficient sensitivity or have not been tested for their ability to detect and distinguish T. solium and T. saginata eggs.
There is a need for compositions and methods that allow sensitive, rapid and noninvasive diagnosis that can differentiate the two species of Taenia, thereby allowing identification of Taenia solium carriers, who can then be treated.